Prosecutors say a Barrington man accused of fatally shooting his estranged girlfriend in the chest Sunday “savagely beat her with a baseball bat” before opening fire. William R. Zientek, 46, of the 400 block of West Russell Street, was ordered held at Cook County Jail following a detention hearing Wednesday before Judge Ellen Mandeltort at the Rolling Meadows courthouse.Zientek is charged with first-degree murder in the slaying of endocrinologist Olga Duchon. During Wednesday’s hearing, Cook County Assistant State's Attorney Robert Mack said Zientek invited Duchon to his home to have a discussion and killed her with a gun he had reported stolen. Zientek’s attorney, Thomas Glasgow, claims the shooting was in self-defense.Mack told the judge the couple’s relationship ended in 2021 over Duchon’s objections to Zientek purchasing and storing firearms in their home. Mack said the pair were parents of a 3-year-old child. Duchon obtained an order of protection against the defendant that required him to surrender his firearms, Mack said. That order revoked his Firearm Owner’s Identification card.Video shows her arriving at Zientek’s home with a tote bag containing leftovers and baked goods about 5:18 p.m. Sunday. Prosecutors say Zientek struck Duchon with a baseball bat, once in the back of the head and once on the top of her head, fracturing her skull, Mack said. He then shot Duchon, Mack said. For more, go to dailyherald.com.